Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations exist, so the description must disclose behavior fully. It claims to split hostnames, yet the schema accepts 9 unrelated parameters (ref, city, feed, json, path, zone, query) with descriptions indicating they are 'discarded' or checked. The description does not acknowledge these other functions or clarify how the tool behaves for non-hostname inputs, making the tool's actual behavior opaque and potentially misleading.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, tight sentence with no wasted words. It front-loads the primary action and includes a useful qualifier. However, it is so short that it sacrifices necessary detail, which is a minor structural drawback.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has 9 optional parameters, no output schema, and no annotations. The description only explains one narrow function (hostname splitting) and omits any guidance on the other 8 parameters, error handling, return format, or use cases. This is severely incomplete for a tool of this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% – every parameter has a description in the schema, so the baseline is 3. The tool description adds no parameter-specific meaning beyond the schema, and does not clarify how the hostname parameter relates to the others. No extra semantic value is provided.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a clear action ('split a hostname into labels') and adds a differentiating caveat ('without WHOIS or ownership data'), which helps distinguish it from ownership-oriented tools. It does not explicitly reference sibling shape tools like github-repo-shape or jira-key-shape, but the core purpose is unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The only guidance is the negative clause 'without WHOIS or ownership data', implying an alternative for WHOIS but never naming one. There is no statement of when to use this tool versus other shape checkers, nor any mention of prerequisites or expected input types beyond the schema. An agent gets little direction on selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.